1. Field of the Invention
This invention relates to dental adhesive compositions which have excellent bonding properties and are useful in bonding living dental tissues to materials (such as metals, organic polymers and ceramics) used for the restoration thereof
2. Description of the Prior Art
In the field of dental materials, a variety of materials have conventionally been used for the purpose of restoring carious teeth (also called decayed teeth) and missing teeth. Such materials include metals such as gold, silver, platinum, alloys and amalgam; organic high polymers such as polymethyl methacrylate, polycarbonate, cured products of multifunctional vinyl resins, and composite resins; and ceramic such as porcelain and implant materials. However, these materials are inherently incapable of adhering to living tooth tissues. Accordingly, in order to achieve bonding between restorative materials and living tooth tissues, there have been proposed a number of dental adhesive compositions containing, as the adhesive component, a compound having any of various polar groups (such as a phosphate group, hydroxyl group or acid anhydride group) with the intention of improving their interaction with the principal inorganic components, such as apatite (a calcium phosphate), or principal organic components, such as collagen (a protein), constituting the tooth tissues.
When the aforesaid prior art adhesive compositions are used to bond a restorative material to living tooth tissues, they have considerable adhesivity to enamel, but completely fail to exhibit adhesivity to dentin. This is due to the physical and chemical structures of living dentin. Specifically, dentin has a structure in which a vast number of dentinal tubules are penetrated and filled with a body fluid. Moreover, dentin contains a fairly high proportion of proteins such as collagen, as compared with enamel. Thus, it may be said that, from the viewpoint of bonding, dentin is in a very adverse environment. Accordingly, the aforesaid prior art adhesive compositions require pretreatment of the principal inorganic component as apatite, with an etching agent (such as phosphoric acid) so as to produce the so-called anchoring effect which brings about a certain degree of bonding to living dentin. Nevertheless, because of the insufficiency of bond strength, a gap will be produced between the restorative material and the dentin over a long time and, in the worst case, the restorative material may even fall off. Thus, the prior art adhesive compositions cannot be said to have bonding properties adequate for practical purposes.